Compatibility of commercial steels with amorphous silicon solar cells; A smart solution based on SiO X sol-gel. Mari-Fe Menéndez, Luis J. Andrés, D. Gómez, P. Sanchez Fundación ITMA 1 PVSAT-12, 6-8 April 2016, Liverpool

2 1. STEELPV project Concept and objectives Work plan 2. Intermediate layer developments Wet strategy based on SiO x sol-gel a-Si:H TFSC deposition 3. Conclusions PVSAT-12, 6-8 April 2016, Liverpool Outline

3 Project title: Sustainable Steels for Direct Deposition of Photovoltaic Solar Cells Acronym: STEELPV ( Call: RFCS (TGS5: Finishing and coating) Duration: 39 months (from 01 July 2014 – 30 September 2017) Total budget: € PVSAT-12, 6-8 April 2016, Liverpool STEELPV: Generalities

4 To functionalize low cost industrial steels as direct substrates for Thin Film Photovoltaic (TFPV) devices. Aim of the project Innovation -To propose new steel substrates for PV. -To make viable thicker steel substrates for PV. -To reduce the steel substrate cost lcomparing with current solar grade stainless stee. -To propose new steel substrates for PV. -To make viable thicker steel substrates for PV. -To reduce the steel substrate cost lcomparing with current solar grade stainless stee. Sectors Building Integrated PV, Road infrastructures, Transports Building Integrated PV, Road infrastructures, Transports PVSAT-12, 6-8 April 2016, Liverpool STEELPV: Concept and objectives

5 PVSAT-12, 6-8 April 2016, Liverpool STEELPV: Work plan

R a < 0.2  m R z < 1.5  m PVSAT-12, 6-8 April 2016, Liverpool - Cost: IL margin respecting to the maximum affordable cost for TFSC application. - Compatibility with lab-scale and up-scale coating machines. Low cost rolling process AISI430 : ~ 2000€/ton (1mm) DX51D+Z : ~ 900€/ton (1mm) DX51D+AS : ~ 950€/ton (1mm) DC01 : ~ 850€/ton (1mm) Steel thickness selection and processing 0.3 mm thick 6 - Decrease the native roughness to a one affordable for all the IL approaches.

Intermediate layer development -Levelling the steel Surface -High quality TFSC deposition -Monolithic TFSC serial interconnection -Antidiffusion barrier -Avoid Steel element diffusion -High TFSC efficiencies -Dielectric barrier -Avoid shunts -Monolithic TFSC serial interconnection € steel +rolling + IL < 0.1 €/W IL requirements: to match steels with TFSC -Stability -TFSC vacuum processes: no desorption -TFSC temperature processes: no degradation PVSAT-12, 6-8 April 2016, Liverpool 7

-Single layer PVSAT-12, 6-8 April 2016, Liverpool Intermediate layer development: Sol-gel strategy -Thermal treatment tuning -210ºC and 550ºC Hydrolisis Condensation SiO x sol-gel approach -Low cost: few precursors -One step acid catalysis at room temperature -Stable sol (no viscosity increase) - Formulation - Application 8 + +

F1 formulation TEOS, MTES, H 2 O, PEG6000, HNO 3 Molar ratios: TEOS/MTES= 1.35, H 2 O/(MTES+TEOS)= 4.7, PEG/(MTES+TEOS)= 0.02 Several days stable in solution -Single layer of ~ 1.3  m free of cracks -No significant decrease of the roughness -No electric insulation due to the low thickness -Hardness pencil (ISO48269) -Adhesion (pull-off) -Homogenous IL layer PVSAT-12, 6-8 April 2016, Liverpool Intermediate layer development: Sol-gel strategy SiOx sol-gel approach 1 hour10 hours24 hours96 hours Viscosity (Pa.s) Spin coating technique Hot-plate curing (210ºC and 550ºC)

-Homogeneous single layer of 3- 4  m free of cracks -Hardness, adhesion are ok -Compatible with hotplate and convection furnace annealing. PVSAT-12, 6-8 April 2016, Liverpool Intermediate layer development: Sol-gel strategy Spin coating technique Hot-plate and convection curing (210ºC) 10 SiOx sol-gel approach F2 formulation TEOS, MTES, H 2 O, PEG6000, HNO 3 + PVP10000 Molar ratios: PVP/(MTES+TEOS)= 0.02 Few hours stable in solution Only 210ºC curing 0.16 €/W

11 Electrical insulation: breakdown voltaje measurement PVSAT-12, 6-8 April 2016, Liverpool > 53V Intermediate layer development: Sol-gel strategy Viability for a monolithic TFSC serial interconnection

PVSAT-12, 6-8 April 2016, Liverpool a-Si:H nip single junction: 1cm 2 12 Intermediate layer development: Sol-gel strategy Steel 0.3mm Ag (400nm) ITO (200nm) a-Si:H (350nnm) ITO (500nm) Ag (400nm) SiOx IL (3-4  m) LayerGas mixture Substrate temperature (ºC) Pressure (mTorr) p-layer SiH 4, B 2 H 6, CH 4, H i-layerSiH n-layerSiH 4, PH 3, H

Isc (mA) Voc (mV) FFPCE (%) Reference cell (substrate=glass) AISI IL * AISI IL DX51D +Z + IL DC01 + IL DX51D+AS + IL * * without Ag grid PCE similar between the four steels and glass PVSAT-12, 6-8 April 2016, Liverpool 13 Intermediate layer development: Sol-gel strategy PCE% = 5.59% DX51D+Z + IL Demonstration of compatibility between the four steels selected and a-Si:H TFSC through sol-gel based on SiOx

14 Scalable process Procedure: 1st find the critical thickness Dip coating (F1 formulation) AISI430 mm/min mm PVSAT-12, 6-8 April 2016, Liverpool Intermediate layer development: Sol-gel strategy

15 AISI430 DC01 -Homogeneous single layer of 3  m free of cracks -Hardness, adhesion are ok -Electric insulation is ok after deposition of Al pad >53V PVSAT-12, 6-8 April 2016, Liverpool Intermediate layer development: Sol-gel strategy Dip coating (F1 formulation) Extraction:230mm/min 0.08 €/W

PVSAT-12, 6-8 April 2016, Liverpool 16 Intermediate layer development: Sol-gel strategy PCE% = 4.90% AISI430 + IL PCE% = 5.21% DC01 + IL

17 PVSAT-12, 6-8 April 2016, Liverpool 1- Sol-gel based on SiO x is a viable approach to match commercial steels with a-Si:H TFSC. - Steel levelling (Rz<200nm), - Good dielectric behaviour, - No delamination observed. - Low cost ( €/W) - a-Si:H (1cm 2 ) were successfully grown on the four steel/IL devices 2- Dip coating showed great results and is a potential up-scaling technique. Conclusions

STEELPV_RFSR-CT Sustainable Steels for Direct Deposition of Photovoltaic Solar Cells Thank you for your attention 18 The research leading to these results has received funding from the European Union’s Research Fund for Coal and Steel (RFCS) research programme under grant agreement nº RFSR-CT PVSAT-12, 6-8 April 2016, Liverpool